Pictures of my inlet ports....

4.2 V8 32v Naturally Aspirated - 414 bhp
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ArthurPE
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Post by ArthurPE » Sun May 09, 2010 11:37 pm

mark758 wrote:I think it is an interesting point raised....the RS5 has an RS4 engine with an upgraded intake system....Are there any other changes?
It would seem to make very liitle commercial sense to make an existing problem worse?
the engine appears to be mechanically identical, with some minor changes
the biggest being the intake and software...

the only 'fix' would be tighter valve stem seals/guides, but some oil has to get under/through them or they will score the stem, it gets wiped off on the far side and builds up on the valve...on other than DI engines the fuel washes it off so it doesn't accumulate...

honestly, I see no way around it (if you keep DI)...if they are tighter, it will just take longer to build up, but it will build up...imo the benefits far outweigh the downsides...

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Post by P_G » Sun May 09, 2010 11:39 pm

Dependent on which source you read the engine is identical bar double intake and dual throttle bodies and some mapping to being 4/5 of an R8 V10 FSI engine. If it is FSI I suspect they will all have a degree of CB. Find a V10 Spyder person to open up their intake manifold or one on a C6 RS6 since it also has FSI if you can. I suspect also on the latter forced induction may be preventative of CB but that is just a guess.

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Post by ArthurPE » Sun May 09, 2010 11:49 pm

P_G wrote:Dependent on which source you read the engine is identical bar double intake and dual throttle bodies and some mapping to being 4/5 of an R8 V10 FSI engine. If it is FSI I suspect they will all havea degree of CB. Find a V10 Spyder person to open up their intake manifold or one on a C6 RS6 since it also has FSI if you can. I suspect also on the latter forced induction may be preventative of CB but that is just a guess.
the turbo comment is interesting...
it's the same size 4.2 liter
has 3 valves/cylinder, area? maybe larger
but must have 50% more airflow if boost ~7.5 psi
more air, same area = higher velocity
perhaps the increased velocity is enough to blow the oil off?
the same mechanism I feel limits growth, area gets smaller, velocity gets higher, limiting deposition

surely someones inspected the valves on one of these...

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Post by P_G » Mon May 10, 2010 12:13 am

I've not seen anything like these discussions on R8, C6 RS6, TT-RS or B8 S4 threads yet they are all FSI?

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Post by ArthurPE » Mon May 10, 2010 12:18 am

P_G wrote:I've not seen anything like these discussions on R8, C6 RS6, TT-RS or B8 S4 threads yet they are all FSI?
TT is a turbo correct?
S4 supercharged
both pretty new and both would have higher velocities due to boost...

a lot of the VW turbo cars suffer from it, iirc

you'ld expect the R8 to have the same issue?

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Post by ArthurPE » Mon May 10, 2010 12:36 am

found all the spec for VAG engines including Lambo
current http://en.wikipedia.org/wiki/List_of_Vo ... gines#C6S6
discontinued http://en.wikipedia.org/wiki/List_of_di ... ngines#BCY
RS4 V8 and R8 V10 bore/stroke 84.5 by 92.8 identical
Lambo V10 82.5 by 92.8 different

since the RS5 displacement is the same (exactly) as the RS4, its engine and the R8 V10 are both based on the RS4

the RS4 valaves are much larger than I thought 1.28" vs 1", even less impact from deposits...the area 30% larger, velocity 30% lower, pressure drop 12% lower...

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Post by ArthurPE » Mon May 10, 2010 12:57 am


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Post by PetrolDave » Mon May 10, 2010 7:29 pm

Sims wrote:
PetrolDave wrote:
ArthurPE wrote:and believing it to be an issue doesn't make it true (nor a 'bad' person)

:D

1 they are fine
2 they don't make more power
3 how would deposits <beep> timing?
4 how would deposits casue 'ping', especilly since it pulled timing only marginally?
5 to minimize it, keep it below the threshhold where it MAY become an issue, that limit is very high...
6 to increase power and mpg, nothing to do with deposits, that's internet selective interpretatio, not from Audi
Second all that.
Why am I not surprised :lol:
Having worked for several years for a well known automotive consultancy that makes a large proportion of its income from designing engines for the major car manufacturers, I guess it's not surprising that I recognise someone who knows what they are talking about. Take a bow ArthurPE.

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Post by ArthurPE » Mon May 10, 2010 7:44 pm

PetrolDave wrote:
Sims wrote:
PetrolDave wrote: Second all that.
Why am I not surprised :lol:
Having worked for several years for a well known automotive consultancy that makes a large proportion of its income from designing engines for the major car manufacturers, I guess it's not surprising that I recognise someone who knows what they are talking about. Take a bow ArthurPE.
why thank you sir...and coming from someone who not only understands the basics, but the complexities of the systems at play, it has special significance...

now I'm fairly sure someone will give us crap over an innocent exchange of mutual respect, but so be it...

folks, if I thought this was an issue of any significance, I would be the first to 'take it to Audi', but I honestly believe it is not, and not only because I 'feel' it, but because ~30 years of experience involving the application, rating, selection, troubleshooting of prime movers, tells me it isn't...

and please, stop assailing anyone who dares to concur with my assessment...
Dave has a vast knowledge base/education/experience concerning these matters and draws his own conclusions, undoubtedly more sorted out than mine...

he obviously has more sense than I, as indicated by his restraint in getting 'sucked into' this BS

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Post by SR71 » Mon May 10, 2010 11:08 pm

I might counter, Dave, by saying that, as a PhD in Unsteady Aerodynamics, who has worked for Airbus, QinetiQ+NASA, FTE @ Boscombe Down (albeit as a contractor working on the JSF) amongst others, I'm quite happy to believe my own conclusions about what deposits do to airflow, the difference being that I'm quite sure the Navier Stokes are fairly complicated last time I looked and they often yield odd solutions, if indeed you can solve them in the first place.

When I did my PhD I used to leave simulations running for days and days (not enough computing power on the University servers) to yield a solution and I was "only" using nonlinear indicial responses as opposed to full CFD.

Granted it was F/A-18 aerodynamics not the internal combustion engine...so we're talking about $50 million dollar products not $55K ones so the value of small margins of "extra performance" is that much more important....still I digress and it was a long time ago...

The debate has lost a degree of lustre I agree...

But I'm curious...

Would you object then if a manufacturer managed to build a DI engine that didn't deposit so much carbon in its manifold?

That'd be presumably a waste of time would it?

I don't understand why anyone would not consider such an engine a better product?

Thats what we're talking about.

Prior to DI, it was never acceptable to have that kind of material "floating" around in an engine that close to some expensive moving parts...

Why now?

People can make their own mind up about the performance delta. In fact I think there is even consensus on that....1-2% perhaps? Maybe even a bit more?

I wonder if the Veyron suffers?

;-)
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Post by Dom81 » Mon May 10, 2010 11:21 pm

SR71 wrote:as a PhD in Unsteady Aerodynamics
So you pilots learn to fly bumpy - I always thought it was the weather...
2007 Daytona RS4 Avant

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Post by ArthurPE » Mon May 10, 2010 11:23 pm

the velocity is < 65 ft/sec thru the torus...very low...the valves are larger than I thought and lift a bit larger...
I agree, in extreme cases, maybe 1 to 2%, 4 to 8HP, maybe, but I still can't come to any conclusion why it would diminish power at all...
definitely not 'feelable', and not measureable by any of the rolling roads in current use
probably iffy even on an engine dyno...

no where near the 40 to 70 HP figures being bandied about...

I'm sure all DI engines suffer to one degree or another, even port injection does over a long enough interval...

better product?: a 12.5:1 Cr on pump gas, 420 HP from 4.2 liter, a wide torque band 90% from 2500 to redline...
yet decent mileage (for a 4000 lb car with >400 HP)

ALL engineering is a balance of compromises...
Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe...Albert Einstein

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Post by mark758 » Tue May 11, 2010 12:01 am

ArthurPE wrote: now I'm fairly sure someone will give us crap over an innocent exchange of mutual respect, but so be it...
“Great minds discuss ideas; Average minds discuss events; Small minds discuss peopleâ€
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Post by ArthurPE » Tue May 11, 2010 12:11 am

mark758 wrote:
ArthurPE wrote: now I'm fairly sure someone will give us crap over an innocent exchange of mutual respect, but so be it...
“Great minds discuss ideas; Average minds discuss events; Small minds discuss peopleâ€

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Post by silverRS4 » Tue May 11, 2010 1:48 am

Not to disrupt the cerebral back-patting, but how about we look at something else besides airflow for a moment. We can even make it hypothetical, so that it doesn't get dismissed with a simple "well, that will simply never happen". Lets say a DI engine is suffering from misfires upon cold start up. There are no misfires during normal operation. Sometimes the total misfire count is only 8-10 in the first 30 seconds after startup (below the threshold for a CEL), but sometimes its 40-50, or even as high as 200-300 misfires, in which case the CEL/MIL will flash, but then go off. Then the valves are cleaned. Misfires are logged for the next 15 cold starts. Not a single misfire occurs. Another significant change is noted in the ignition timing. The average level of retardation has dropped, so after the valve cleaning, the actual timing is closer to the target, or set point. Question - what does a clean set of valves have to do with less cold start misfires and less retardation in a DI engine with closed-loop knock control? Added info - closed-loop knock control is used to achieve peak cylinder pressure (and torque) with a variety of fuel grades in addition to detecting detonation (knock).

I'll save the back-patting until someone gives a good effort at answering a direct question, hypothetical or not. If there are no takers...well,that's OK too.

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